Effect of roving Effect of roving on spatial release from masking on spatial release from masking

for amplitude-modulated for amplitude-modulated noise stimulinoise stimuli

Norbert Kopčo*, Jaclyn J. Jacobson, and Barbara Shinn-Cunningham

Hearing Research CenterDepartment of Cognitive and Neural Systems

Boston University

*Technická univerzita, Košice, Slovakia and Dartmouth College

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Introduction

Spatial Release from Masking (SRM):

Detectability of a masked Target sound improves when Target (T) and Masker (M) are spatially separated

Study the interaction between spatial processing (SRM) and temporal modulation processing when detecting masked stimuli

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Goals

Question 1: How does presence of modulation in T or M influence SRM?

E.g., is SRM larger when T only modulated or when M only modulated?

Question 2: What cues/factors determine performance?

E.g.: space, temporal modulation, grouping.

Performed 2 experiments, differing in Masker level uncertainty.

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Methods: Stimuli

Target (T) – white noise 300-8000 Hz, 200 msMasker (M) – white noise 200-12000 Hz, 300 ms30-ms cos2 rampsT temporally centered in M40-Hz sinusoidal amplitude modulation, depth of 0.5

Example: modulated T in (nominally) non-modulated M:

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Methods: Modulation Conditions

Modulation type:

no modulation

T / M modulated in phase

only T modulated

only M modulated

T / M modulated out of phase

Envelope:

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Methods: Spatial ConfigurationsVirtual auditory space, non-individualized anechoic HRTFs,

distance 1m

Five spatial configurations:

SeparatedCo-located

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Exp 1 Methods: general

- 7 normal hearing listeners

- Threshold TMR in 25 different conditions (5 spatial x 5 modulation)

- 5 repeats per subject per condition (+ 1 practice)

- 3I-2AFC procedure, adapting T level; M level fixed

Analysis:- collapse data across co-located and separated configurations- plot across-subject mean threshold TMR and within-subject standard error of mean

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5

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-(thr

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ld T

MR

) [dB

]

noIPSmNmSNmOOP

Results of Experiment 1

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Compared to no modulation ( ), presence of modulation can decrease ( ), increase ( ), or not change ( ) SRM. Effect is small (up to 2 dB).

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5

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15

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-(thr

esho

ld T

MR

) [dB

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noIPSmNmSNmOOP

Perceptual Learning in Exp 1

Perceptual learning observed in all conditions, but with varying size. Effect of modulation on SRM is small in first repeat ( ) but large in last ( )

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1st vs. 5th repeat

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Exp 1: SummaryPerceptual learning observed over course of

experiment, causing growing differences in the effect of modulation on SRM.

At the end, compared to no-modulation:- SRM grows with T modulation (2 dB)- SRM decreases with M modulation or T/M modulation out-of-phase (2 dB)- small effect of co-modulation

Candidate cues:- modulation (detected in periphery or in IC)- space (SOC)- space / modulation as grouping cues- increase in level

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Exp 2: Intro

Goal: Which cues determine which thresholds

Introduce Masker level uncertainty - Eliminate across-interval overall level change cue:M level roved by ±5 dB between intervals within a 3I-2AFC trial (T level roved as well to keep TMR constant)

Otherwise Exp 2 identical to Exp 1 (7 new subjs).

Results: Observed perceptual learning similar to Exp 1. Next, show only results of last repeat.

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0

5

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-(thr

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ld T

MR

) [dB

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noSNmIPSmNmSNmOOP

Results: Exp 1 & Exp 2 – last repeat

Left: Rove has huge effect when no modulation or space cue available, small effect when modulation cue only available, no effect when space cue avail.

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0

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-(thr

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MR

) [dB

]

noSNmIPSmNmSNmOOP

Results: Exp 1 & Exp 2 – last repeat

Right: Results w/ no modulation ( ) cue are rove-level dependent. Results w/ modulation ( ) are independent of rove, except for a constant shift.

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SummaryFor broadband noise T masked by broadband noise M:

When T and M are co-located:- T-modulated threshold is worse than M-mod threshold, which is worse than the T/M-mod-out-of-phase threshold- non-mod thresholds are M-level dependent

When T and M are separated:- trends are similar, but differences smaller- non-mod thresholds are worse than mod-thresholds

Perceptual asymmetry:SRM when detecting absence/reduction in modulation is

smaller (by 4 dB) than SRM when detecting presence/increase in modulation.

Possible mechanism:Non-linear combination of space and modulation cues.

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SummaryPerceptual learning was observed, and it was stronger for

some combinations of spatial/modulation conditions than for others

Different strategies/cues are used for detection of presence vs. absence of modulation.

Effects might be larger after more learning.

Masker level uncertainty - influenced detection when overall stimulus level was the only detection cue, and, to a lesser extent, when modulation cue was available. - did not influence detection when space cue was available.

Very few of these effects can be explained by considering only mechanisms of peripheral/brainstem auditory processing.